1. Technical Field
The present invention relates to a liquid ejecting head for ejecting droplets from a nozzle in response to the displacement of a piezoelectric element, a liquid ejecting apparatus, and an actuator that includes a piezoelectric element.
2. Related Art
A representative example of liquid ejecting heads for ejecting droplets is an ink jet recording head. A typical ink jet recording head includes a piezoelectric element disposed on a flow passage forming substrate with a diaphragm interposed therebetween. The flow passage forming substrate includes a pressure generating chamber. The piezoelectric element includes a lower electrode, a piezoelectric layer, and an upper electrode. A displacement of the piezoelectric element generates pressure in the pressure generating chamber, allowing the ink jet recording head to eject ink droplets from a nozzle. It is known that the displacement characteristics of a piezoelectric element used in such an ink jet recording head depend greatly on the crystalline orientation of a piezoelectric layer. Thus, in some proposed piezoelectric elements, the crystals of a piezoelectric layer are appropriately orientated to improve the displacement characteristics (see, for example, JP-A-2004-66600).
In some piezoelectric elements that include a lower electrode, a piezoelectric layer, and an upper electrode, the piezoelectric layer tapers downward at its ends (tapered surfaces) (see, for example, JP-A-2007-118193).
In a piezoelectric element described in JP-A-2007-118193, although no upper electrode is formed on inclined end faces (hereinafter referred to as a tapered portion) of a piezoelectric layer, a lower electrode is continuously disposed across a plurality of piezoelectric elements. Thus, the tapered portion of the piezoelectric layer undergoes a strong driving electric field and may be damaged.
In piezoelectric elements described in JP-A-2004-66600 and JP-A-2007-118193, a lower electrode is continuously disposed across a plurality of piezoelectric elements. In other piezoelectric elements, a lower electrode is patterned for each piezoelectric element, and a piezoelectric layer extends to the outside of the lower electrode (for example, JP-A-2000-32653).
In a piezoelectric element described in JP-A-2000-32653, a tapered portion of a piezoelectric layer does not undergo a strong driving electric field and may not be damaged by the driving electric field. However, when a piezoelectric layer described in JP-A-2004-66600 is applied to a piezoelectric element described in JP-A-2000-32653 to improve the displacement characteristics of the piezoelectric element, the piezoelectric layer may be damaged around an end of a lower electrode during the operation of the piezoelectric element probably because of a difference in crystallinity between one portion of the piezoelectric layer on the lower electrode and the other portion of the piezoelectric layer outside the lower electrode (on a diaphragm).
Such problems may occur not only in ink jet recording heads for ejecting ink droplets, but also in other liquid ejecting heads for ejecting droplets and actuators that include a piezoelectric element. Furthermore, the piezoelectric element may have a low response speed and may be difficult to drive at a high speed.